Eye movement is defined as the rotational movements about three axes with respect to the eye in the primary position: an axis for vertical movements (X axes); an axis for horizontal movements perpendicular to the first axis (Z axis); and an axis for torsional movements about the line of sight (Y axis). To record these three axes' rotational eye movements accurately, three-dimensional analysis of the movements is necessary. Until very recently, however, few methods of analysis have been reported. In this paper, the significance of three-dimensional analysis of eye movements is discussed with the use of actual three-dimensional analysis data, and our own analysis system.
The purpose of this study was to determine the normal limits of canal paresis (CP) and directional preponderance (DP) in the bithermal caloric test. Data were collected from two groups. Group I consisted of 23 young normal subjects. Group II consisted of 89 patients selected from a total of 405 patients referred, because of attacks of vertigo, for pure tone audiometory and vestibular testing to determine the nature of vestibular and/or cochlear disturbances. The maximum eye speeds of the slow phase of all four irrigations were calculated from Jongkees' formula. The normal range corresponded to the mean±2 standard deviations in each group. The results showed that the normal limits of CP and of DP should be set at ±25% and ±19% respectively, in group I, and ±33% and ±33%, respectively, in group II.
Ten patients (5 male, 5 female) with acoustic neurinoma underwent stereotactic radiosurgery with a gamma unit. Their ages ranged from 29 to 68 years (mean, 52 years). The follow-up periods were 20 to 38 months (mean, 26 months). The doses delivered to the tumor were 9.9 to 13.5 Gy at the periphery and 17 to 30 Gy at the center. Neuroimaging studies showed that 6 tumors became smaller, 3 were unchanged, and 1 was larger. Severe complications such as hydrocephalus were not seen. Hearing was presereved with a change in the pure tone audiometric threshold of 10 dB or less in 6 of the 8 patients tested. One patient became deaf 5 months after surgery. His CT scan had shown large cysts in the tumor before surgery. Indications for this type of therapy for such patients must be decided cautiously.
In Miyazaki Medical College, students have been taught the same equilibrium func-tion tests for the past 15 years. We analyzed the data to determine whether or not the pro-gram is adequate for undergraduate medical education. Most of the 108 students could perform Romberg's test, goniometry, static sen-sography, and the pointing test, Vertical writing and Gait tests were also performed suc-cessfully. But 22.2% of them recorded incorrect data for moving distance in the stepping test possibly because of influences of noise and light. Caloric testing is the most difficult equilibrium function test, but the data obtained were reliable. All students had a keen interest in equilibrium function and understood the tests, because they had experienced them as both examiners and as examinees. We are satisfied that the curriculum is suitable for undergraduate medical education.
Optokinetic training (OKT) is known to improve optokinetic nystagmus (OKN), but little is known about the mechanism. To elucidate the mechanism, we examined the effect of OKT on OKN in pigmented rabbits. The rabbits received OKT (a step stimulus of 30 deg/sec, for 15 min a day) for 3 weeks. The OKN of the rabbits was tested with a step stimulus (1, 2, 5, 10, 20, 30, 45 deg/sec) once a week; we also examined the effect on training of injections of methamphetamine. OKT significantly increased the average steady state gain with the step stimulus but did not significantly change either the time to the steady state or the duration of optokinetic after-nystagmus (OKAN). Metham-phetamine (0.5 mg/kg i.p.) reduced the time to the steady state, before and after the 3-week training period, but did not significantly change the average steady state gain or the duration of OKAN. These results suggest that the oculomotor pathway, except for the velocity storage mechanism, may be responsible for the improvement seen with optokinetic training.
To evaluate the involvement of N-methyl-D-aspartic acid (NMDA) receptors in the optokinetic training (OKT)-induced improvement of optokinetic nystagmus (OKN), we examined the effect on the optokinetic reflex of MK-801 ((±)-5-metyl-10, 11-dihydro-5H-dibenzo [a, d] cyclohepten-5, 10-imine maleate). Experiments were performed on pigmented rabbits in which OKN had been improved by OKT for 12 days. When MK-801 was injected intramuscularly, OKN was blocked; this blockade was completely reversed within 72 hrs. At non-intoxic doses (0.05 and 0.1 mg/kg), this drug caused an in-crease in locomotor activity and a reduction of OKN. On the other hand, neither the postrotatory nystagmus (PRN) nor the electroencephalogram (EEG) of the cerebral neocortex and hippocampus was influenced by non-intoxic doses of MK-801. A similar effect was observed on both atropine-sensitive and atropine-resistant EEGs. These results indicate that MK-801-induced impairment of OKN is probably due to its inhibition of NMDA receptors in the oculomotor pathway, suggesting that the activation of this recep-tor may be involved in the improvement of OKN by OKT.
The purpose of this study is to make clear the significance of locus length per unit area (total locus length/ area of sway, L/A) as a parameter of stabilometry. We examined 100 healthy subjects aged 6 to 73 years. The subject stands on a stabilometer with eyes open or closed, and the sway of the center of gravity of the body is recorded for one minute. The pattern and area of sway, total locus length, L/A, Romberg's coefficient and power spectrum are recorded, and the L/A and other parameters are correlated. 1) The L/A with eyes closed was low in those less than 20 years of age, higher at age 20 to 50. After age 60, these were some individual differences. 2) The values of L/A with eyes closed were similar to those with eyes open. 3) The L/A showed a negative correlation with the area of sway and the RMS. 4) The L/A was not related to total locus length or Romberg's coefficient. 5) Subjects with a high L/A had a high density power spectrum at 2-5 Hz. These findings show that L/A is a parameter of the fine control of standing posture by proprioceptive reflexes. The L/A is useful in the examination of the regulation of stan-ding posture.
An equilibrium test battery was performed in 28 patients who had received cochlear implants in our institute in the last 4 years. A total of 13 patients complained of dizziness after the operation. They were divided into three groups according to the time course of dizziness; dizziness occurring immediately after the operation and disappeared within two weeks (immediate type); lasting more than two weeks in 2 patients (prolonged type); in 4 patients it occurred more than one month after the operation (late onset type). Patients who had no dizziness after the operation had a lower response to caloric testing than did those who experienced dizziness. The cause of dizziness was judged to be due to a peripheral lesion in the immediate and prolonged groups, but in only 1 patient of the late onset group.
Six healthy female volunteers were trained with the rail stance test. They were asked to do 30 trials of rail stance every day for a maximum of 60 seconds with their eyes open. The training effect was evaluated by the stance time. Training ceased when stance time reached 60 s in more than half of the 30 trials. A follow-up study was done every week for one month to investigate the retention of training. Both the training effect and the retention of training showed large inter-individual differences. In addition, the retention of training showed a positive highly correlation with the duration of training required to attain the goal. The faster the progress during training, the higher the ability after training. We conclude that the speed of training and the retention of equilibrium function depend on a kind of memory in the brain, which is inherent and individually different.